The invention relates to a hybrid gas generator for an air bag.
A hybrid gas generator is known from EP 0 616 578 B1 which contains a gas-generating solid charge and a storage gas. In the event of initiation, the solid material charge is ignited by an ignition element. As a result of this, a sliding piston is advanced in the direction of the storage chamber. The sliding piston contains a first bursting disc, and the closing element of the storage chamber represents a second bursting disc. After the ignition of the solid charge, the second bursting disc which closes the storage chamber is to be destroyed first, so that cold gas arrives in the air bag. The second bursting disc is to be destroyed thereafter by means of the pressure which continues to build up in the combustion chamber, so that hot gas penetrates into the storage chamber and heats the storage gas still present there. The proper functioning of this gas generator depends on the bursting behaviour of the two bursting discs. In particular the bursting disc provided at the sliding piston must be destroyed at a precisely defined pressure. The bursting disc provided at the sliding piston must open in dependence upon the pressure of the combustion gases, whereas the bursting disc which closes the storage chamber is destroyed in dependence upon the path of the sliding piston. These different dependencies have the result that the pressure build-up behaviour of the gas generator can be subjected to considerable manufacturing tolerances. The characteristic of the pressure increase in the combustion chamber and the burning characteristic must be carefully matched to the strength of the predetermined breaking points of the bursting discs, with the result that the manufacture of the gas generator requires very high levels of precision.